Technical Field
The present disclosure relates to the fabrication of nanometer-sized integrated circuit field effect transistor (FET) devices and, in particular, to devices that incorporate quantum dot films to control electrical characteristics of the devices.
Description of the Related Art
As technology nodes for integrated circuits scale below 10 nm, maintaining precise control of various electrical characteristics in bulk semiconductor devices becomes increasingly more challenging. Bulk semiconductor devices include, for example, metal-oxide-semiconductor field effect transistors (MOSFETs). A MOSFET is a three-terminal switching device that includes a source, a gate, and a drain. MOSFETs are interconnected by a network of wires through contacts to each of the source, drain, and gate terminals.
When a voltage exceeding a certain threshold voltage (Vt) is applied to the MOSFET gate, the device switches on so that an electric current flows through a channel between the source and the drain. The value of Vt depends, in part, on the characteristic energy band structure of the semiconductor material and, in particular, on a characteristic band gap which represents the amount of energy needed to boost a valence electron into the conduction band, where the electron can participate as a charge carrier in the channel current. The source and drain regions are typically doped with ions that serve as charge reservoirs for the device. Device performance parameters such as switching speed and on-resistance are largely dependent upon control of doping concentrations and the locations (e.g., depth profiles) of the dopants in the substrate after implantation and/or after annealing implanted regions at high temperatures.
Present technology challenges include, for example, achieving desirable dopant concentrations in the source and drain (S/D) regions, maintaining low S/D contact resistance, preventing short channel effects (SCE), improving drain-induced barrier lowering (DIBL), controlling Vt, and controlling a characteristic sub-threshold slope (SS). Strained silicon transistors address some of these challenges by replacing bulk silicon in the source and drain regions with epitaxially-grown silicon compounds. Strained silicon presents one alternative to ion doping, and therefore circumvents problems associated with controlling dopant concentrations and profiles. Introducing strain into the silicon crystal of a MOSFET tends to increase charge mobility in the channel region, thereby improving performance. However, strained silicon and other new technologies fail to address all of the technology challenges listed above.